The present invention concerns an aircraft collision-avoidance device, used notably to avoid ground collision by controlling the angle of descent. It is applicable in particular to airliners during final approach to landing. More generally, it is applicable to all aircraft which, during their missions, must fly close to the ground, for example, close to mountains, or make significant changes in altitude in areas where there is a risk of ground collision, whether the aircraft be in take-off phase, level flight or landing.
Ground collision-avoidance devices already exist and they are characterized mainly by their use of radio-altimeters and computers giving the barometric height based on measurements of pressure and temperature, and navigation means such as inertial systems or flight management systems. The principle of such devices lies in the use of an altimetric height, measured with respect to the ground, in association with variations of altimetric or barometric height. The use of barometric height variations is preferred over altimetric variations owing to their better precision at large altitudes. The distance from the ground is compared with a threshold value which depends on the height and configuration of the aircraft, allowing for the position of the undercarriage, flaps or nose, for example. When the measured data, notably height and its variation as a function of time, exceed certain thresholds a warning signal is sent to the crew. However, such devices tend to generate the warnings too late to enable the crew to react in time to avoid a collision. Another disadvantage of known devices is that they frequently trigger false alarms, for example when over-flying, at safe altitude, ground with localized peaks which in fact present no danger. This problem seriously reduces the credibility of such collision-avoidance devices.
Improvements have been made to these devices, in particular by introducing databases enabling the threshold values to be modulated as a function of the geographic location of the aircraft, thus reducing the number of false alarms. However, the database must be adapted to each type of terrain. In the future, we could anticipate systems equipped with digital models of the ground, enabling the position of the aircraft and the nature of the ground over which it will be flying to be known at all times. Nevertheless the use of such models requires databases of sufficient precision, which implies considerable memory capacity. Furthermore, the problems of data input and update of such systems complicates their use and, in view of the large volumes of data to be memorized, the risk of error is non-negligible.
Finally, another problem is that in order to limit the risk of false alarms known collision-avoidance devices are frequently disabled by the crew below a certain altitude, notable during approach to landing, since the aircraft must by necessity approach the ground while maintaining a substantially straight flight path, notably avoiding vertical changes in altitude owing to the presence of obstacles on the ground.